Realtek HD Sony Vaio internal microphone stopped working

Hi,
I have a Sony Vaio, nearly a year old. Yesterday I was using Audacity to record some vocals and the microphone was working fine. Today I tried recording something again and the microphone wasn't working. I got into the control panel to fix the settings (to check whether it was muted or had the volume turned down) but it wasn't that. It does recognize the microphone and after rebooting my computer it works for a second and then it goes dead and stops recognizing. It doesn't work with any audio recording application. I even tried restoring the system to an earlier version, but it still doesn't work.
Please help!
Thanks in advance.